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Although uncommon as a distinct clinical entity, osteosarcoma is the most frequently (70% to 80%) identified primary bone tumor in cats. Metastatic rates in cats (5% to 10%) are lower than those reported in dogs (80% to 90%), and wide surgical excision offers longer survival rates.

This retrospective study from two European veterinary schools evaluated the effects of histologic and clinical characteristics on prognosis for feline osteosarcoma, along with a histologic comparison to phenotypically similar canine osteosarcoma lesions. The authors reviewed the medical records of 62 cats (1994 to 2004) with histologically confirmed osteosarcoma and 22 dogs (1985 to 1999) with histologically confirmed skeletal osteosarcoma of the same location and subtype that corresponded to 22 of the feline skeletal osteosarcoma cases.

The study results revealed that the cats exhibited more axial (25) than appendicular (15) lesions and more skeletal (40) than extraskeletal (22) tumors. Results also revealed that feline osteosarcoma was most frequently identified in the maxilla (seven cases) and interscapular region (five cases) and that feline skeletal osteosarcoma was histologically similar to canine skeletal osteosarcoma. The cats had a tumor recurrence rate of 44% after surgery and a metastatic rate of 10%. A poorer prognosis was seen in cats with incomplete surgical resection, increased histologic grade, and increased mitotic index. Although vascular invasion by osteosarcoma was high in the cats in this study (82%) and is associated with a high-grade tumor and poor prognosis in dogs with osteosarcoma, it was not a significant prognosticator for feline osteosarcoma. The authors concluded that feline and canine skeletal osteosarcoma share similar histologic characteristics yet different prognostic characteristics.

COMMENTARY

In cats, axial osteosarcoma carries a poorer prognosis than appendicular or extraskeletal forms, probably because of difficulty in surgical excision. From this report, histologic analysis of tissues in cats with osteosarcoma will aid clinicians in providing a prognosis for owners, especially if incomplete surgical resection (unclean margins) occurs. Because feline osteosarcoma lesions have not been as frequently described as canine osteosarcoma lesions, reporting survival rates for patients in this study would have been beneficial.